Equilibrium and Le Chatelier\'s Principle PDF

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Equilibrium and Le Chatelier's Principle lab...

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Equilibrium and Le Chatelier’s Principle Due: March 1, 2021 CHEM 1110

Purpose: The purpose of this laboratory experiment is to study the effects of stress on two systems’ equilibrium using Le Chatelier’s principle. Theory/Principles: When a reaction reaches chemical equilibrium, the forward reaction will be equal to the reverse reaction. A system at equilibrium can change when stress is added to the system. Stress includes changes in temperature, pressure, or concentration. When stress is added to a system, the system will shift in order to minimize the change the stress is causing and return the reaction back to equilibrium. This is known as Le Chatelier’s principle. This causes for the either the forward or reverse reaction to be increased temporarily, resulting in new concentrations for the reactants and products. When stress is added to the reactants, it will cause for the reaction to shift to the right which means it will be shifting towards to the products causing for an increase in product concentrations. When stress is added to the products, it will shift to the left towards the reactants having the opposite effect. Stresses added to the system can be measured by observing any color changes of the reaction and by measuring the absorbance of a reaction through a spectrophotometer. Procedure: Procedure followed exactly as steps in the lab manual. Results and Discussion: Data obtained from video. Table 1. Part 1 Test Tube

Change Introduced

Reaction Response 2 CrO42- (aq)

2 H+ (aq)

↔ Cr2O72- (aq)

H2O (l)

1.

HCl added

↓

↓

↑

↑

1.a

NaOH added

↑

↑

↓

↓

2.

HCl added

↓

↓

↑

↑

2.a

NaOH added

↑

↑

↓

↓

3.

NaOH added

↑

↑

↓

↓

3.a

HCl added

↓

↓

↑

↑

4.

NaOH added

↑

↑

↓

↓

4.a

HCl added

↓

↓

↑

↑

5.

NaOH and Ba2+ added

↑

↑

↓

↓

5.a

HCl added

↓

↓

↑

↑

6.

HCl and Ba2+ added

↓

↓

↑

↑

6.a

NaOH added

↓

↓

↑

↑

7.

Ba2+ added

↑

↑

↓

↓

8.

Ba2+ added

↓

↓

↑

↑

Table 2. Part 2 Test Tube

Absorbance

Change Introduced

Color Observations

Shift from Equilibrium (toward reactants or products) Standard/reference Toward product

3 drops water

Blue color change N/A

1 drop Pb(NO3)2

N/A

Toward reactant

Placed in hot water bath Placed in ice water

Blue color change N/A

Toward product

655 nm 1.

N/A 0.690

2.

HCl added 0.794

3.

Toward reactant

0.367 4. 0.545 5. 2.35 6.

Toward reactant

0.23

bath

In Table 1, 1 M HCl was added to 0.1 M CrO42- and the solution turned orange meaning the reaction favored the products. 1 M NaOH was also added to CrO42- and turned yellow meaning the reaction favors the reactants. 1M HCl was then added to 0.1 M Cr2O72- and the solution turned orange favoring the products. 1 M NaOH was then also added to Cr2O72- and the solution turned yellow favoring the reactants. NaOH was again added to CrO42- and the solution again turned yellow. Followed by this, HCl was again added to CrO42- and the solution turned orange. NaOH and HCl were again added to the Cr2O72- and the solutions turned yellow and orange, respectively. A few drops of NaOH and Ba2+ were added to 0.1 M CrO42- and the solution turned yellow. HCl was then added and the solution turned orange. Oppositely, a few drops of HCl and Ba2+ were added to 0.1 M Cr2O72- and the solution turned orange. NaOH was then added the solution remained orange and did not experience a color change. For the last two reactions, 0.1 Ba2+ was added to both CrO42- and Cr2O72- and turned yellow and orange respectively. In Table 2, the addition of HCl caused the solution of 0.05 M [CoCl4]2- and distilled water to turn blue which shifts the reaction towards the products, following Le Chatelier’s principle. Adding 3 drops of water did not have an effect on the color of the system. 1 drop of Pb(NO3)2 caused for a precipitate to form but did not have an effect on the color change of the system. The placement of the solution in the hot and ice water bath turned the solution blue shifting it to the left and had no effect on the color change, respectively. The reaction turned from a pink color to a blue color which can be used to determine that the solution is endothermic.

Conclusion:

The purpose of this laboratory experiment is to examine the effects of stress on a system’s equilibrium. Through using Le Chatelier’s principle, the shifts in the system were able to be determined from each stress added to the system.

References

Chem 1010 lab manual University of Louisiana at Monroe. This lab was prepared by Vicki Kubo-Anderson and Errol V. Mathias http://www.digipac.ca...